| Summary: | 碩士 === 國立彰化師範大學 === 電子工程學系 === 95 === In this thesis, circularly polarized (CP) antennas with broadband as well as with wide beamwidth are designed and investigated. For the broadband circular- polarization antenna design, the CP antenna dimension is made suited for operating in WLAN 5.8 GHz band. A rectangular metal strip is used to connect the curl metal strip and the feed-pin strip. The impedance of the antenna can then be controlled by tuning the width of the rectangular metal strip. Besides, in order to cover both of the 5.2 GHz (5150-5350 MHz) and 5.8 GHz (5725-5875 MHz) bands, the bandwidth of the proposed antenna needs to be 750 MHz (about 13.4 %). In this thesis, we also propose an L-shape planar metal antenna to cover the whole 5 GHz band. The disadvantage of the CP radiation is improved by varying the antenna structure. Measured results show that a good radiation pattern of the L-shape planar metal antenna were achieved.
For the circularly polarized antenna with a wide beamwidth, the center frequency of the operating band is designed at 1.575 GHz (which is in the GPS band). The CP antenna uses a corner-truncated square patch as its radiating element to obtain the CP radiation characteristic. Then the beamwidth is increased by adding a pyramidal-horn ground plane to the antenna structure. It also shows that a folded conducting wall extended from the pyramidal-horn ground plane can further broaden the beamwidth. Such a design requires a smaller height of the pyramidal-horn ground plane, and thus can reduce the antenna dimension. Results obtained in this research can be applied to microwave communication system. The technique presented in this research is expected to serve as a useful reference for 3-D antenna designers.
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